Picture the following scenario: On a hot and humid summer Friday, you join the exodus from the oppressive D.C. metro area and head to Ocean City, Maryland. You leave work early, so traffic on the Bay Bridge isn't too bad and you cover the 150 miles in a little more than three hours. On Saturday, you spend a pleasant day at the beach. That night, an unexpected storm hits the area, with record winds and raging surf. Sunday is rainy, so you pack up to leave early. You turn on the radio to hear the latest traffic report. Astonished, you learn that the Bay Bridge has sustained severe damage in last night's weather; the twin bridges are being evaluated for structural damage and both spans are closed to all traffic. You weigh your options. You can head south and take the bridge connecting the Eastern Shore to Cape Henry, Virginia, or you can head north and cross over from Delaware to Chesapeake City, Maryland. After a quick consultation with a map, you learn that the Virginia route will take roughly 7 hours (without traffic) and is roughly 370 miles. The Delaware route is quicker — about 4-5 hours to cover 210 miles. Resigned to a long and frustrating trip, you get in your car and start driving north toward Delaware. The trip home is no longer straightforward.

Ecosystems work in a similar manner. When an ecological regime reaches a tipping point, goes over the edge, and settles into a new stable state, it will often sustain fundamental changes that make it virtually impossible to go back along the same path. A return is still achievable, but the route back might be longer and much more circuitous than anticipated. Ecologists call this hysteresis: the loss of a symmetrical pathway between two stable states of an ecological system.

These functional changes that accompany regime shifts present a clear challenge for restoration efforts. In many northern lakes, for example, high phosphorus input from sewage, industrial, and agricultural sources can cause a switch from a state characterized by low phytoplankton biomass and clear water to one with high phytoplankton biomass, cloudy water, high phosphorus regeneration from sediments, and anoxic conditions for living organisms. "Once the tipping point is reached for these lakes, the cost of going back is enormous," says limnologist Steve Carpenter at the University of Wisconsin-Madison. "To revert to the original state, it is necessary to reduce the phosphorus to a lower level than it was before the shift occurred in the first place."

So what does this mean for restoration efforts in the Chesapeake Bay? Lost ecological buffers, such as oyster reefs, underwater grasses and forested coastlines, combined with changed land use are clear signs that the road home will follow a different route. The Chesapeake 2000 agreement, a historic partnership between Virginia, Maryland, Pennsylvania, the District of Columbia, the Chesapeake Bay Commission and the U.S. Environmental Protection Agency signed in 1983 and 1987, outlines a time frame over which to restore the Bay in an integrated and coordinated manner — with clear benchmarks for progress, such as new water quality standards for oxygen and water clarity by 2010. Recent criticism of the Chesapeake Bay Program's modeling efforts, however, suggests that the Bay is not responding as quickly as predicted. Could loss of a symmetric road back (hysteresis) be the culprit?

There are, in fact, clear signs that metaphorically washed out bridges may already be a problem for the Bay. In a recent Estuaries paper, UMCES scientists Walter Boynton and James Hagy (now with the Environmental Protection Agency) present a long-term analysis of low oxygen (hypoxia) in the Bay from 1950 to 2001. They found that moderate hypoxia has increased almost three-fold for an average flow year over that time period. Furthermore, they found that the relationship between nitrogen influx (nutrient loading) and hypoxia is nonlinear — meaning that for a given amount of nitrogen the volume of low oxygen water is greater than can be explained by the quantity of nitrogen alone.

This relationship is both intriguing and troubling, UMCES president Don Boesch reported in his testimony to the U.S. House of Representatives Committee on Government Reform at a hearing held in August. It suggests that the Bay appears to have lost some of its ability to assimilate nutrients without becoming seriously hypoxic, possibly because of long-term losses of species in the benthic community. "This diminished resilience probably means that we simply have to accomplish much more reduction in nutrient loading before we see greatly reduced hypoxia," Boesch testified to the committee.

"In general, it may take considerable action to move the Bay along a restoration trajectory," Boesch says. "A linear ratcheting back along the curve may not be possible; it may require more to reverse the decline of the Bay than it took to get there in the first place. So, in the short run, the slope of recovery may be steeper, but there are ledges along the way and these ledges might be self-sustaining," he says.

Angie Hengst sits on the edge of the boat and quickly pulls on a skin suit. She draws a mask and snorkel over her face and slides into the water, holding a cylindrical gray tube in one hand and a buoyant float attached to a piece of PVC pipe in the other. She could stand easily in the four feet of water in Broad Creek on Maryland's Eastern Shore, but wears a mask and snorkel to make repeated surface dives to embed a sampler, called a "peeper," into the mucky substrate.

Hengst, a graduate student with researcher Laura Murray at Horn Point Laboratory, is surveying the geochemistry of the sediment in beds of underwater grasses. She is trying to determine whether one species of grass, Ruppia maritime, modifies its environment chemically and, if so, whether it makes conditions more favorable for other species of underwater grass to grow. Since Ruppia is one of the only species to have made a significant comeback so far, Murray and Hengst, along with systems ecologist Michael Kemp, are trying to determine if it could serve as a pioneer species of sorts. They ask whether Ruppia could make the sediment more hospitable for other species to colonize, if planted through active restoration efforts.

Feeling around in the mucky substrate, graduate student Angie Hengst (above right) tries to locate the edge of a bed of underwater grass, Ruppia maritime (shown at left, below). Faculty research assistant Debbie Hinkle (above left) holds a marker float and the "peeper" (shown at left, above) they will embed in the mud to measure sediment chemistry. They will retrieve the device and its data in 10 days time.

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